1. Field of the Invention
The invention relates to a workpiece holder.
2. Background Art
A workpiece that is to be machined in several steps of working on various machine tools is fixed in the machine tools by means of chucking appliances for being machined on a workpiece holder. For an ensuing step of working on the following machine tool to be performed, it is detached from the workpiece holder and transported to the following machine tool where it is again fixed on a workpiece holder.
U.S. Pat. No. 3,606,300 teaches a workpiece rest with a workpiece aligned and fixed on it. To this end, the workpiece rest has quite a number of holes. The workpieces and the workpiece rest that carries them are transported together from one machine tool to the next, nothing being said on how fixing takes place on the individual machine tools.
It is known from U.S. Pat. No. 5,558,784 to fix a work that is to be machined on a workpiece rest. The workpiece rest possesses chucking elements in the form of twistlocks which simultaneously constitute centering elements for at least roughly centering and distinctly aligning the workpiece rest on the processing machine tool, it being absolutely necessary to fit the workpiece rest accurately into the machine tool. In the machine tool, the coordinate values i.e., the position of the workpiece rests in the three-dimensional system of coordinates, are measured and offset against the data stored in the machine tool in order for the precise position of the workpiece to be obtained in relation to the coordinate systems of the machine tool.
This familiar method exhibits several drawbacks in installations with various machine tools, for instance transfer machines, or short-cycle flexible manufacturing systems, because the periods needed for accurately fitting in the workpiece rests add to the cycle times of the entire installation.
It is an object of the invention to embody a workpiece holder that does not require any accurate fitting of the workpiece during or after the chucking process.
According to the invention, this object is attained in a workpiece holder, comprising a workpiece holding fixture; and a workpiece rest; wherein the workpiece rest is provided with arrangements for fixing a workpiece in a given position relative to the workpiece rest; wherein the workpiece holding fixture is provided with bearing surfaces and the workpiece rest with counterpart surfaces that rest on the bearing surfaces for the workpiece rest to have an accurately given position in a first, second and third coordinate direction; and wherein chucking appliances are provided, chucking the workpiece rest relative to the workpiece holding fixture in the first, second and third coordinate direction. The workpiece takes an accurately defined position on the workpiece rest and keeps this position throughout the steps of machining. When transported from one machine tool to the other, the workpiece rest is chucked accurately in all the three coordinate directions, there being no need for renewed fitting of the workpiece into a machine tool.
Further features, advantages and details of the invention will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing.